25/03/2025
I asked one of my students to define 'Matter' and he said, "Matter is anything that has weight and occupies space."
His definition, though incorrect, was understandable because both mass and weight are closely related and are used the same way in our everyday lives. It's a common experience to hear people say, "I weigh 60kg, 40kg, etc... But wait🤔!! You follow dey make this mistake as a scientist? How can your weight be measured with the unit of mass? 😱
These quantities (weight and mass) are not the same; they refer to two quantities in Physics. So the correct definition of matter is: Matter is anything that has mass and occupies space.
In this article, we are going to critically examine these quantities and identify the key differences between them. It may be quite long, but it is worth your time.
How do I even explain this in a way that someone who is not a scientist/science student would understand?💭🤔
Take, for example, a scenario where you go to a supermarket to buy something, and you place the items you buy into a basket. Let’s assume that before buying anything, the mass of the basket was 1 kg. After purchasing items such as a tin of milk weighing 3 kg, a tin of Milo weighing 2 kg, and a packet of Golden Morn weighing 4 kg, the total mass of the system (basket + items) would be:
Total mass = mass of basket + mass of milk tin + mass of Milo tin + mass of Golden Morn packet
Total mass = 1 kg + 3 kg + 2 kg + 4 kg
Total mass = 10 kg (the quantity of matter present)
Therefore, Mass can be defined as the quantity of matter in a body.
Now, where does weight come in? 🤔
When you first picked up the basket, it felt light and easy to carry. You could swing it back and forth. However, after filling the basket with items from the market, it became heavier. And the moment you try to lift it, you feel a downward pull on your hand—this downward pull is the weight of the basket, caused by gravity."
Therefore, weight can be defined as the force acting on a body due to the earth's gravitation.
RELATIONSHIP BETWEEN WEIGHT AND MASS
If the basket is so heavy that the downward pull (weight) on your hand becomes too much to bear, you might decide to use another basket to redistribute the load. By doing this, you will notice that the basket becomes easier to carry, and the pull on your hand is reduced. Everyone has experienced this situation, but what distinguishes a scientist is their ability to ask and answer the questions surrounding such events.
You must have seen a Christian mother who broke a chair when she attempted to sit on it 😂🤣😂. When I say 'Christian mother', I believe you understand what I mean - the heavyweights in C.W.O. Then, you are at one corner, maintaining steeze and resisting the urge to laugh out loud, but in your mind, laughter wan finish you. Then you tell your friend 'this woman suppose know say this chair no fit carry her weight.' In other words, the chair couldn't resist the downward force she exerted when she sat on it. So, the force she exerted on the chair when she sat on it was her weight. Then, her body size or how heavy she appears represents her mass.
On the other hand, if a slim mama sits on the same chair, the weight (downward force) she exerts on the chair won't have any effect. What do these scenarios tell you?
It simply shows that if the mass of a body is increasing, the weight (downward force) of the body also increases, and if the mass of a body is decreasing, the weight of the body also decreases at the same rate. So, physicists use the proportionality statement to make this point simple. We say 'Mass is directly proportional to weight', and this can be represented mathematically as:
W ∝ m ...... (i)
Where,
∝ = the proportionality sign
So, what is that single statement which distinguishes mass from weight?
Answer: Mass refers to the quantity of matter in a body, while weight refers to how heavy the body is.
OTHER DIFFERENCES BETWEEN MASS AND WEIGHT INCLUDE:
1. The mass of a body is always constant regardless of location, but the weight of a body changes with respect to location
Back to our story, imagine that the Christian mother has a mass of 100 kg. No matter where she is - at home, in the market, or even in another country - her mass remains 100 kg. This means that mass does not change with location. How can we get her weight?
Let's invoke our mathematical expression:
Recall: W ∝ m …… (i)
When you remove the proportionality sign (∝) and replace it with an equal sign, a constant (g) appears; this constant is known as the acceleration due to gravity, hence (i) becomes:
W = mg....... (ii)
Where
W = weight
m = mass
g = acceleration due to gravity
Remember, we said that g is a constant - meaning that it has a specific value.
On Earth, the acceleration due to gravity, g = 9.8m/s². So the weight of our Christian mother is:
W = mg
W = 100kg × 9.8 m/s² = 980N
What happens when the Christian mother goes to the Moon?
It's still her now!! Her 100kg remains the same, but what happens to weight?
Acceleration due to gravity on the Moon is = 1.6 m/s²
Therefore, her weight on the Moon becomes:
W = 100kg × 1.6 m/s² = 160N
You gerrit?😉
From what we have gathered, we discovered that for the same woman with a mass of 100 kg, her weight was 980 N (heavier) on Earth and 160 N (much lighter) on the Moon. Therefore, this supports the claim that the mass of a body is always constant, regardless of location, but the weight of a body changes with respect to location.
2. The second difference between weight and mass is that weight is a vector quantity while mass is a scalar quantity
A scalar quantity is a quantity that has magnitude but no direction. Imagine our Christian mother whose mass was 100kg; this information only quantifies how much matter is contained in her makeup. It doesn't tell us in which direction she is moving or where she is located.
On the other hand, a vector quantity is a quantity which has both magnitude and direction. Weight is a vector quantity because it is directed towards the earth (downward). If you try to lift this woman who has a mass of 100kg, you will experience a downward force on your arms. This downward force is the weight of the woman. This tells us that weight has magnitude (980N in the case of the woman) and acts in the downward direction.
3. Weight is measured in newtons (N), while mass is measured in kilograms
4. The instrument used for measuring weight is a spring balance or weighing scale, while the instrument for measuring mass is a beam or chemical balance.
In conclusion, mass and weight are two different quantities and should not be used interchangeably. In my next article, I will explain why it is incorrect to say “Matter is anything that has weight and occupies space”
